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Thread: ClassCastException: Vehicle cannot be cast to java.base/java.lang.Comparable

  1. #1
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    Default ClassCastException: Vehicle cannot be cast to java.base/java.lang.Comparable

    package HRT;
     
    import java.util.TreeSet;
     
    public class Vehicle {
        String type ;
         double speed;
     
     
        public Vehicle() {
            type = "bicycle";
            speed = 20.0 ;
        }
        public Vehicle(String type, double speed) {
            this.type= type ;
            this.speed=speed;
        }
     
     
     
    public static String setType(String type)   {
        return type;
    }
    public static double setSpeed(double speed) {
        return speed;
     
    }
    public void speedUp() {
        speed = speed *2;
     
    }
    public void speedDown() {
        speed = speed/2 ;
     
    }
     
    }
     
    package HRT;
     
    import java.util.TreeSet;
     
     
    public static void partB() {
             String[] typeArray = {"car", "train", "plane", "bicycle",};
             double[] speedArray = {60, 180, 1000, 20};
             TreeSet vehicles = new TreeSet<>();
             for(int i = 0; i < typeArray.length; i++) {
             vehicles.add(new Vehicle(typeArray[i], speedArray[i]));
             }
            }
     
    public static void main(String[] args) { 
            Exercise4.partB();
        }   
    }


    How can I modify the class Vehicle to make the program run correctly ?
    I don't understand why i get this ClassCastException
    can anyone help please ?

  2. #2
    Member John Joe's Avatar
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    Default Re: ClassCastException: Vehicle cannot be cast to java.base/java.lang.Comparable

    Vehicle class need to implement Comparable interface
    Whatever you are, be a good one

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    Default Re: ClassCastException: Vehicle cannot be cast to java.base/java.lang.Comparable

    Is this correct?


    package HRT;
     
    import java.util.TreeSet;
     
    public class Vehicle implements Comparable {
    	String type ;
    	 double speed;
     
     
    	public Vehicle() {
    		type = "bicycle";
    		speed = 20.0 ;
    	}
    	public Vehicle(String type, double speed) {
    		this.type= type ;
    		this.speed=speed;
    	}
     
     
     
    public static String setType(String type)	{
    	return type;
    }
    public static double setSpeed(double speed) {
    	return speed;
     
    }
    public void speedUp() {
    	speed = speed *2;
     
    }
    public void speedDown() {
    	speed = speed/2 ;
     
    }
     
    public int compareTo(Object temp) {
    	Vehicle other = (Vehicle) temp;
    	if (speed > other.speed)
    	{
    		return 1;
    	}
    	else if(speed < other.speed) {
    		return -1;
    	}
    	else return 0;
     
     
    }
     
    }

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    Default Re: ClassCastException: Vehicle cannot be cast to java.base/java.lang.Comparable

    Any errors ? Is the output is desired output ?
    Whatever you are, be a good one

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    Default Re: ClassCastException: Vehicle cannot be cast to java.base/java.lang.Comparable

    First, your Vehicle class is designed incorrectly.

    1. Your setters are not setting anything but returning something. Setters should not be static
    and should have a return type of void.

    2. You need to add some getters to properly get the value. They should not be static either.

    3. Implementing Comparable is fine and I believe you did it okay. But it is not required. You could also
    have defined a Comparator for Vehicle and passed it to the TreeSet constructor as follows:


    Comparator<Vehicle> comp = Comparator.comparing(Vehicle::getSpeed);
    // then later
    TreeSet<Vehicle> set = new TreeSet<>(comp);

    Regards,
    Jim

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